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adiabatic equation - 2.5 2c SWA

Stewart Mason
I don't get involved with adiabatic equations all to often, hence I'm a bit rusty! I'm trying to calculate the R1+R2 for a 2 core 2.5mm SWA. Obviously the R1 is the easy bit, I'm struggling with the SWA as the R2.  I saw a link to a table on the old forum but I can't find it now. Any ideas?


Thanks Stewart
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    °Zoomup:




    Zoomup:

    Without doing any calculations and just using previous "experience knowledge" I venture to say that the proposed installation as described will comply.


    But I may be concerned about Volt drop. What is the design load and installation method?


    Z.




    CORRECTION. Now, after doing some quick sums I now believe that the disconnection time will be nearer to 10 seconds with an earth fault of negligible impedance at the far end of the S.W.A. That just shows us what guessing can achieve.......bad results. The C.P.C. needs to be bigger, supplemented with an additional copper C.P.C. or an R.C.D. installed at the origin of the circuit.


    Z.


     




    How so Z?


    A B16 as Max Zs of 2.73 Ω for 0.4 s disconnection

    Less Ze of 0.35 Ω leaves 2.38 Ω

    So, using even the over-excessive final temperature resistances leaves over 90 m to achieve disconnection time of 0.4 s (although for Type B mcb this is the same as 5 s) ???

    The limiting factor as you initially said would be volt-drop at 45 m (if it's a final circuit conductor, less if you want to drop short circuits off the other end).

Reply
  • 0

    °Zoomup:




    Zoomup:

    Without doing any calculations and just using previous "experience knowledge" I venture to say that the proposed installation as described will comply.


    But I may be concerned about Volt drop. What is the design load and installation method?


    Z.




    CORRECTION. Now, after doing some quick sums I now believe that the disconnection time will be nearer to 10 seconds with an earth fault of negligible impedance at the far end of the S.W.A. That just shows us what guessing can achieve.......bad results. The C.P.C. needs to be bigger, supplemented with an additional copper C.P.C. or an R.C.D. installed at the origin of the circuit.


    Z.


     




    How so Z?


    A B16 as Max Zs of 2.73 Ω for 0.4 s disconnection

    Less Ze of 0.35 Ω leaves 2.38 Ω

    So, using even the over-excessive final temperature resistances leaves over 90 m to achieve disconnection time of 0.4 s (although for Type B mcb this is the same as 5 s) ???

    The limiting factor as you initially said would be volt-drop at 45 m (if it's a final circuit conductor, less if you want to drop short circuits off the other end).

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